1. Field of the Invention
This invention relates to testing of the mechanical operation of spring powered switches such as medium voltage circuit breakers.
2. Background Information
Switches carrying sizable electric currents, such as medium voltage circuit breakers, require substantial mechanical forces to operate the switch rapidly and to hold the contacts closed against the magnetic repulsion forces generated by the current. In a typical medium voltage circuit breaker, a set of charged closing springs is released to close the breaker and to charge an opening spring which, in turn, is later released to open the breaker. The speed at which the mechanism operates is so rapid that it is difficult to identify the nature of any malfunctions, or even in some cases, to discern that the breaker is not operating properly.
Under typical practice, a skilled engineer is dispatched to the field or the circuit breaker must be returned to the factory to determine the cause and remedy for a malfunction or inferior performance. Due to the high inertia developed in the operating mechanism, there is considerable overshoot and distortion of the parts during operation. Often, analysis, which typically is performed using an expensive camera system, is qualitative rather than quantitative (e.g., it is determined that there is excessive overshoot, but no measurement of the amount of overshoot is provided). This technique for analyzing the operation of such switches is expensive and time consuming, and is highly dependent upon the skill and experience of the tester.
U.S. Pat. No. 5,726,367 discloses a method and apparatus for testing the operation of a spring powered switch mounted in a support frame and operated by an operating mechanism having driven parts actuated by release of charged springs. A recording medium, such as a tape, is applied to one of the driven parts. A fixture mounted to the support frame adjacent the selected driven part supports a marking instrument in contact with the recording medium at a fixed point relative to the support frame. When the charged spring is released, the selected driven part, which carries the recording medium, moves relative to the marking instrument. This produces a trace on the recording medium representing the movement of the selected driven part relative to the fixed point. This trace provides a quantitative record of the movement of the selected driven part which can be used to analyze the performance of the operating mechanism of the switch.
N. Anger et al., "Diagnostics/Monitoring for Medium-Voltage Components and Systems", pp. 1.14.1-1.14.4, discloses the detection of the angle of rotation curve for the breaker shaft of a vacuum circuit breaker's spring-stored-energy operating mechanism. An expert circuit breaker diagnostic system employs temperature sensors, current transformers, and an angle resolver to provide temperatures, opening and closing solenoid coil currents and charging motor currents, and shaft angles to a microprocessor in a continuous on-line operation. Trend analyses are performed using parameters of individual past switching operations with the aid of temperature, voltage and time-compensated classification models.
Although it is known to employ mechanical or electronic sensors for sensing movement of certain operating mechanism components to test a circuit breaker, there remains a need, however, for an improved method and apparatus for accurately testing spring operated switches.
There is a more particular need for such an improved method and apparatus which can be easily used by unskilled personnel.
There is another more particular need for such an improved method and apparatus which is inexpensive and can, therefore, be economically repeated frequently.